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  • Nitrogen fixation  (62)
  • Springer  (62)
  • Elsevier
  • 2015-2019
  • 2010-2014
  • 1985-1989  (62)
  • 1989  (19)
  • 1986  (43)
Collection
Publisher
  • Springer  (62)
  • Elsevier
Years
  • 2015-2019
  • 2010-2014
  • 1985-1989  (62)
Year
  • 1
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    Biology and fertility of soils 8 (1989), S. 356-368 
    ISSN: 1432-0789
    Keywords: Plant-root associations ; Azospirillum spp ; Rhizosphere ; Nitrogen fixation ; Acetylene reduction assay (ARA) ; Phytohormones
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Bacteria of the genus Azospirillum are extensively studied for their plant-growth promoting effect following inoculation. Physiological and biochemical studies of these diazotrophic bacteria are now benefiting from recent breakthroughs in the development of genetic tools for Azospirilum. Moreover, the identification and cloning of Azospirillum genes involved in N2 fixation, plant interaction, and phytohormone production have given new life to many research projects on Azospirillum. The finding that Azospirillum genes can complement specific mutations in other intensively studied rhizosphere bacteria like Rhizobia will certainly trigger the exploration of new areas in rhizosphere biology. Therefore a review of the Azospirillum-plant interactions is particularly timely.
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  • 2
    ISSN: 1432-0789
    Keywords: Nodule damage ; Rivellia angulata ; Nitrogen fixation ; Cajanus cajan ; Pigeonpea ; Vertisol
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Damage caused by Rivellia angulata larvae to pigeonpea root nodules at the ICRISAT center in India was greater in the crop grown on Vertisols (up to 86%) compared to that on Alfisols (20%). Attempts to quantify the field effects of nodule damage on growth and yield of pigeonpea in a Vertisol, involving many heavy applications of soil insecticides (aldrin and hexachlorocyclohexane) failed because the insecticides did not control the pest and adversely affected the growth of the pigeonpea and the subsequent crop of sorghum (Sorgorum bicolor L. Moench). The impact of nodule damage on pigeonpea growth, yield and nutrient uptake was successfully studied in greenhouse-grown plants at three N levels. In this pot study, artificial inoculation with Rivellia sp. led to substantial nodule damage (70%). The results of this damage were a significant overall reduction in nodule dry weight (46%), acetylene reduction activity (31%), total leaf area (36%), chlorophyll content of leaves (39%) and shoot dry weight (23%) 68 days after sowing. At maturity, Rivellia sp. infestation caused significant reductions in top dry weight (22%), root and nodule dry weight (27%), seed dry weight (14%), and total N (29%) and P uptake (19%). The problems and prospects of manipulating nodule damage so as to reduce N losses in pigeonpea are discussed.
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  • 3
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    Biology and fertility of soils 7 (1989), S. 269-274 
    ISSN: 1432-0789
    Keywords: Nitrogen fixation ; Frankia-Ceanothus spp. association ; Acetylene reduction assay (ARA) ; Microsymbiont population ; Nodules ; Actinomycetes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Wildland shrub improvement is needed for sound range and disturbed land revegetation practice. The possibility of selecting superior N2-fixingFrankia-Ceanothus spp. actinorhizal associations was examined. Greenhouse tests were used to expose various soil-borne microsymbiont andCeanothus sp. population accessions in reciprocal combination. The acetylene reduction rate was used as a measure of N2-fixation capacity. There was no significant interaction between host and microsymbiont regardless of source for all variables measured. The acetylene reduction rate, nodule number and mass, plant biomass, and root: shoot ratio were significantly different among soil sources. The acetylene reduction rate was not significantly different amongCeanothus sp. accessions. Neither was it strongly correlated with other variables. It was concluded that the N2-fixation rate is more a function ofFrankia sp. than the hostCeanothus sp. in actinorhizal associations. It appears possible to select soil sources with superior N2-fixing microsymbiont populations.
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  • 4
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    Oecologia 79 (1989), S. 566-568 
    ISSN: 1432-1939
    Keywords: Carbon dioxide ; Lichen ; Lobaria ; Nitrogen fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Thalli of Lobaria pulmonaria (L.) Hoffm., a nitrogen-fixing epiphyte common in mesic temperate forests, were collected in a Douglas-fir (Pseudotsuga menziesii Franco) forest near Corvallis, Oregon, and maintained for 20 to 40 days in controlled-environment chambers with atmospheric CO2 concentrations of 374 and 700 μll-1. Nitrogenase activity, which was assayed by the acetylene reduction method, was approximately doubled in the lichen maintained in elevated CO2. Increases in nitrogen fixation by lichens may be an important part of the integrated ecosystem response to rising CO2.
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  • 5
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    Archives of microbiology 146 (1986), S. 239-244 
    ISSN: 1432-072X
    Keywords: Cicer arietinum ; nif Genes ; Plasmids ; Rhizobia ; DNA/DNA hybridization ; Nitrogen fixation ; Chickpeas
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We examined 27 strains of chickpea rhizobia from different geographic origins for indigenous plasmids, location and organization of nitrogen fixation (nif) genes, and cultural properties currently used to separate fast- and slow-growing groups of rhizobia. By using an in-well lysis and electrophoresis procedure one to three plasmids of molecular weights ranging from 35 to higher than 380 Mdal were demonstrated in each of 19 strains, whereas no plasmids were detected in the eight remaining strains. Nitrogenase structural genes homologous to Rhizobium meliloti nifHD, were not detected in plasmids of 26 out of the 27 strains tested. Hybridization of EcoRI digested total DNA from these 26 strains to the nif probe from R. meliloti indicated that the organization of nifHD genes was highly conserved in chickpea rhizobia. The only exception was strain IC-72 M which harboured a plasmid of 140 Mdal with homology to the R. meliloti nif DNA and exhibited also a unique organization of nifHD genes. The chickpea rhizobia strains showed a wide variation of growth rates (generation times ranged from 4.0 to 14.5 h) in yeast extract-mannitol medium but appear to be relatively homogeneous in terms of acid production in this medium and acid reaction in litmus milk. Although strains with fast and slow growth rates were identified, DNA/DNA hybridization experiments using a nifHD-specific probe, and the cultural properties examined so far do not support the separation of chickpea rhizobia into two distinct groups of the classical fast- and slow-growing types of rhizobia.
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  • 6
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    Archives of microbiology 143 (1986), S. 330-336 
    ISSN: 1432-072X
    Keywords: Phototrophic bacteria ; Green sulfur bacteria ; Chtorobium ; Nitrogen fixation ; Nitrogenase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Four strains of the green sulfur bacterium Chlorobium were studied in respect to nitrogen nutrition and nitrogen fixation. All strains grew on ammonia, N2, or glutamine as sole nitrogen sources; certain strains also grew on other amino acids. Acetylene-reducing activity was detectable in all strains grown on N2 or on amino acids (except for glutamine). In N2 grown Chlorobium thiosulfatophilum strain 8327 1 mM ammonia served to “switch-off” nitrogenase activity, but the effect of ammonia was much less dramatic in glutamate or limiting ammonia grown cells. The glutamine synthetase inhibitor methionine sulfoximine inhibited ammonia “switch-off” in all but one strain. Cell extracts of glutamate grown strain 8327 reduced acetylene and required Mg2+ and dithionite, but not Mn2+, for activity. Partially purified preparations of Rhodospirillum rubrum nitrogenase reductase (iron protein) activating enzyme slightly stimulated acetylene reduction in extracts of strain 8327, but no evidence for an indigenous Chlorobium activating enzyme was obtained. The results suggest that certain Chlorobium strains are fairly versatile in their nitrogen nutrition and that at least in vivo, nitrogenase activity in green bacteria is controlled by ammonia in a fashion similar to that described in nonsulfur purple bacteria and in Chromatium.
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  • 7
    ISSN: 1432-072X
    Keywords: Transposon mutagenesis ; Soybean ; Nitrogen fixation ; Root nodules ; Auxotrophy ; Bradyrhizobium japonicum ; Glycine ; Rhizobium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Four histidine auxotrophs of Bradyrhizobium japonicum strain USDA 122 were isolated by random transposon Tn5 mutagenesis. These mutants arose from different, single transposition events as shown by the comparison of EcoRI and XhoI-generated Tn5 flanking sequences of genomic DNA. The mutants grew on minimal medium supplemented with l-histidine or l-histidinol but failed to grow with l-histidinol phosphate. While two of the muants were symbiotically defective and did not form nodules on Glycine max cvs. Lee and Peking and on Glycine soja, the other two mutants were symbiotically competent. Reversion to prototrophy occurred at a frequency of about 10-7 on growth medium without added antibiotics, but prototrophs could not be isolated from growth medium containing 200 μg/ml kanamycin and streptomycin. The prototrophic revertants formed nodules on all the soybean cultivars examined. When histidine was supplied to the plant growth medium, both nodulation deficient mutants formed effective symbioses. On histidine unamended plants, nodules were observed infrequently. Three classes of bacterial colonies were isolated from such infrequent nodules: class 1 were kanamycin resistant-auxotrophs; class 2 were kanamycin sensitive-prototrophs; and class 3 were kanamycin-sensitive auxotrophs. Our results suggest that two Tn5 insertion mutations in B. japonicum leading to histidine auxotrophy, affect nodulation in some way. These mutations are in regions that show no homology to the Rhizobium meliloti common nodulation genes.
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  • 8
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    Archives of microbiology 146 (1986), S. 74-79 
    ISSN: 1432-072X
    Keywords: Azotobacter chroococcum ; Nitrogen fixation ; Nitrogenase genes ; Nif gene reiteration ; Deletion mutagenesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Strains of the obligately aerobic nitrogen fixing organismAzotobacter chroococcum were constructed which contained defined chromosomal deletions in which the nitrogenase structural genenifHDK cluster (nifH for the polypeptide of the Fe-protein component of nitrogenase andnifD andnifK for the alpha and beta subunits respectively of the MoFe-protein component of the enzyme) was replaced by a kanamycin resistance gene. N2 fixation was nevertheless observed in deletion strains though only in a molybdenum-deficient medium or in spontaneously arising tungstate-resistant derivatives. In comparison with the parent strain growing in molybdenum-sufficient medium, diazotrophic growth was slow and the nitrogenase activity in vivo was characterised by disproportionately low rates of C2H2-reduction compared to H2-evolution and relative insensitivity of H2-evolution to inhibition by C2H2. The findings show reiteration of functional structural genes for nitrogenase inA. chroococcum consistent with our previous observation of twonifH genes in this organism and detection in this work of a secondnifK-like sequence in the genomes of both parent and deletion strains whenA. chroococcum nifK DNA was used as a probe.
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  • 9
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    Archives of microbiology 146 (1986), S. 12-18 
    ISSN: 1432-072X
    Keywords: Arctic rhizobia ; Arctic legumes ; Nitrogen fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Forty-eight strains of Rhizobium isolated from the root nodules of three species of legumes indigenous to the high tundra (Astragalus alpinus, Oxytropis maydelliana andOxytropis arctobia) are phenotypically heterogenous with respect to intrinsic antibiotic resistance, expression of nitrogenase activityex planta and plasmid content. All of the strains possess a 250–300 kb plasmid and are homologous to each other on the genomic DNA level but have little DNA homology with selected reference strains of well characterized species of rhizobia. The arctic rhizobia have an optimum growth temperature of 23°C and can grow slowly at 5°C. The DNA from four of the isolates, which were selected for detailed investigation, have sequences homologous tonif andnod genes fromRhizobium trifolii.
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  • 10
    ISSN: 1432-072X
    Keywords: Bradyrhizobium ; Electron microscopy ; Mutants ; Nitrogen fixation ; Nodulation ; Soybean ; Symbiosis ; Transposon Tn5
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The genome of the slow-growing Bradyrhizobium japonicum (strain 110) was mutagenized with transposon Tn5. A total of 1623 kanamycin/streptomycin resistant derivatives were screened in soybean infection tests for nodulation (Nod) and symbiotic nitrogen fixation (Fix). In this report we describe 14 strains possessing a stable, reproducible Nod+Fix- phenotype. These strains were also grown under microaerobic culture conditions to test them for free-living nitrogen fixation activity (Nif). In addition to strains having reduced Fix and Nif activities, there were also strains that had reduced symbiotic Fix activity but were Nif+ ex planta. Analysis of the genomic structure revealed that the majority of the strains had a single Tn5 insertion without any further apparent physical alteration. A few strains had additional insertions (by Tn5 or IS50), or a deletion, or had cointegrated part of the vector used for Tn5 mutagenesis. One of the insertions was found in a known nif gene (nifD) whereas all other mutations seem to affect different, hitherto unknown genes or operons. Several mutant strains had an altered nodulation phenotype, inducing numerous, small, widely distributed nodules. Light and electron microscopy revealed that most of these mutants were defective in different stages of bacteroid development and/or bacteroid persistence. The protein patterns of the mutants were inspected by two-dimensional gel electrophoresis after labelling microaerobic cultures with l-(35S)methionine. Of particular interest were mutants lacking a group of proteins the synthesis of which was known to be under oxygen control. Such strains can be regarded as potential regulatory mutants.
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  • 11
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    Archives of microbiology 145 (1986), S. 159-161 
    ISSN: 1432-072X
    Keywords: Clostridium cellobioparum ; Clostridium thermocellum ; Ammonium assimilation ; Nitrogen fixation ; Nitrogen control
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Inorganic nitrogen metabolism in two cellulose degrading clostridia, the mesophile Clostridium cellobioparum and the thermophile Clostridium thermocellum was investigated. Both strains show acetylene reduction (i.e. possibly nitrogenase activity), contain glutamine synthetase, glutamate dehydrogenase and glutamate-dependent transaminases. C. cellobioparum additionally contains a NADH-dependent glutamate synthase and a NH 4 + -repressible glycine dehydrogenase (NADPH). Remarkably, acetylene reduction in C. thermocellum is not repressed by ammonium, casting doubt whether this activity is due to nitrogenase. The results are compared with the data from other saccharolytic clostridia.
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  • 12
    ISSN: 1432-072X
    Keywords: Heterocyst isolation ; Osmoregulators ; Cyanobacteria ; Nitrogen fixation ; Anabaena variabilis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A method is described for the preparation of cyanobacterial heterocysts with high nitrogen-fixation (acetylene-reduction) activity supported by endogenous reductants. The starting material was Anabaena variabilis ATCC 29413 grown in the light in the presence of fructose. Heterocysts produced from such cyanobacteria were more active than those from photoautotrophically-grown A. variabilis, presumably because higher reserves of carbohydrate were stored within the heterocysts. It proved important to avoid subjecting the cyanobacteria to low temperatures under aerobic conditions, as inhibition of respiration appeared to lead to inactivation of nitrogenase. Low temperatures were not harmful in the absence of O2. A number of potential osmoregulators at various concentrations were tested for use in heterocyst isolation. The optimal concentration (0.2M sucrose) proved to be a compromise between adequate osmotic protection for isolated heterocysts and avoidance of inhibition of nitrogenase by high osmotic strength. Isolated heterocysts without added reductants such as H2 had about half the nitrogen-fixation activity expected on the basis of intact filaments. H2 did not increase the rate of acetylene reduction, suggesting that the supply of reductant from heterocyst metabolism did not limit nitrogen fixation under these conditions. Such heterocysts had linear rates of acetylene reduction for at least 2 h, and retained their full potential for at least 12 h when stored at 0°C under N2.
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  • 13
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    Archives of microbiology 145 (1986), S. 403-407 
    ISSN: 1432-072X
    Keywords: Propene ; 1-Butene ; Xanthobacter ; Mono-oxygenase ; Nitrogen fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Yellow-pigmented bacteria showing typical characteristics of Xanthobacter spp. were isolated from enrichments with propene and 1-butene, using classical techniques. The generation time for growth on propene and 1-butene of these bacteria ranged from 5 to 7h. A NADH-dependent mono-oxygenase was identified in cell-free extract of Xanthobacter Py2. This mono-oxygenase was not influenced by potential inhibitors tested indicating that propene mono-oxygenase is different from other hydrocarbon mono-oxygenases described until now. Nitrogenase activity could be measured using the acetylene reduction assay with propene as energy source, because acetylene did not inhibit the mono-oxygenase activity.
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  • 14
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    Archives of microbiology 151 (1989), S. 445-453 
    ISSN: 1432-072X
    Keywords: Denitrification ; Growth yield measurements ; Nitrate respiration ; Nitrogen fixation ; Proton translocations in respirations ; Azospirillum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract For Azospirillum brasilense Sp7, the energy transformation efficiencies were measured in anaerobic respirations with either nitrate, nitrite or nitrous oxide as respiratory electron acceptors by determining the maximal molar growth yields and the H+-translocations using the oxidant pulse method. In continuous cultures grown with malate limiting, the maximal molar growth yields (Y s max -values) were essentially the same with O2 or N2O but were 1/3 and 2/3 lower with NO 2 - or NO 3 - , respectively, as respiratory electron acceptors. Both the maximal molar growth yields and the maintenance energy coefficients were surprisingly high when Azospirillum was grown with nitrite as the sole electron acceptor and source for N-assimilation. Growth under N2-fixing conditions drastically reduced the Y s max -values in the N2O and O2-respiring cells. In the H+-translocation measurements, the $$\vec H^ + $$ /oxidant ratios were 5.6 for O2→H2O, 2.5–2.8 for NO 3 - →NO 2 - , 2.2 for NO 2 - →N2O and 3.1 for N2O→N2 respirations when the cells were preincubated with valinomycin and K+. All the values were enhanced when the experiments were performed with valinomycin plus methyltriphenylphosphonium (=TPMP+) cation. The uncoupler carbonyl cyanide-m-chlorophenyl-hydrazone diminished the H+-excretion indicating that this translocation was due to vectorial flow across the membrane. In the absence of any ionophore, nitrate and nitrite respirations were accompanied by a H+-uptake $$(NO_3^ - \to N_2 = - 2.9 \vec H^ + /NO_3^ - and NO_2^ - \to N_2 = - 2.5 \vec H^ + /NO_2^ - )$$ . Any significant H+-translocation could not be detected in N2O- and O2-respirations under these conditions. It is concluded that nitrate reduction proceeds inside the cytoplasmic membrane, whereas nitrite is reduced extramembraneously. The data are not conclusive for the location of nitrous oxide reductase. The maximal molar growth yield determinations and the absence of any H+-uptake in untreated cells indicate a cytoplasmic orientation of the enzyme similar to the terminal cytochrome oxidase of respiration. The low H+-extrusion values for N2O-respiration compared to O2-respiration in cells treated with valinomycin plus TPMP+ are, however, not in accord with such an interpretation.
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  • 15
    ISSN: 1432-072X
    Keywords: Bradyrhizobium ; Gene cloning ; Heme ; Marker exchange mutagenesis ; Nitrogen fixation ; Respiration ; Symbiosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Random and site-directed Tn5-induced mutagenesis of Bradyrhizobium japonicum yielded two mutations, one in strain 2960 and the other in strain 2606::Tn5-20, which mapped close to each other but in separate genes. The corresponding wild-type genes were cloned, and their approximate location on the cloned DNA was determined. Mutant 2960 was Fix- and formed green nodules on soybean, whereas strain 2606::Tn5-20 had ca. 4% of wild-type Fix activity and formed white nodules. Cytochrome oxidase assays (Nadi tests) showed a negative reaction with both mutants, indicating a functional deficiency of cytochrome c or its terminal oxidase or both. However, the mutants grew well under aerobic conditions on minimal media with different carbon sources. Furthermore, mutant 2960 had a reduced activity in hydrogen uptake, was unable to grow anaerobically with nitrate as the terminal electron acceptor and 2960-infected soybean nodules contained little, if any, functional leghemoglobin. Southern blot analysis showed that a B. japonicum heme biosynthesis mutant [strain LO505: O'Brian MR, Kirshbom PM, Maier RJ (1987) Proc Natl Acad Sci USA 84: 8390–8393] had its mutation close to the Tn5 insertion site of our mutant 2606::Tn5-20. This finding, combined with the observed phenotypes, suggested that the genes affected in mutants 2960 and 2606::Tn5-20 were involved in some steps of heme biosynthesis thus explaining the pleiotropic respiratory deficiencies of the mutants. Similar to strain LO505, the mutant 2606::Tn5-20 (but not 2960) was defective in the activity of protoporphyrinogen IX oxidase which catalyzes the penultimate step in the heme biosynthesis pathway. This suggests that one of the two cloned genes may code for this enzyme.
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  • 16
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    Archives of microbiology 151 (1989), S. 180-182 
    ISSN: 1432-072X
    Keywords: Klebsiella pneumoniae ; Nitrogen fixation ; nifL ; Regulation ; Oxygen control ; Nitrogen control
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A number of in-frame deletions have been constructed in the Klebsiella pneumoniae regulatory gene nifL. The effects of each nifL mutation on NifA-mediated expression from the nifH promoter of K. pneumoniae have then been assessed with respect to both nitrogen and oxygen control. These experiments indicate that, in contrast to the situation with the homologous regulatory proteins NtrB and NtrC, NifA activity is not impaired in the absence of NifL. We conclude that the only function of NifL is to inactivate NifA in response to an increase in the nitrogen or oxygen status of the cell.
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  • 17
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    Planta 167 (1986), S. 382-386 
    ISSN: 1432-2048
    Keywords: Acetylene/nitrogen molar ratio ; Alnus-Frankia symbiosis ; Nitrogen fixation ; Nitrogenase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Acetylene reduction, 15N2 reduction and H2 evolution were measured in root systems of intact plants of grey alder (Alnus incana (L.) Moench) in symbiosis with Frankia. The ratios of C2H2: 15N2 were compared with C2H2:N2 ratios calculated from C2H2 reduction and H2 evolution, and with C2H2:N2 ratios calculated from accumulated C2H4 production and nitrogen content. It was possible to calculate C2H2:N2 ratios from C2H2 reduction and H2 evolution because this source of Frankia did not show any hydrogenase activity. The ratios obtained using the different methods ranged from 2.72 to 4.42, but these values were not significantly different. It was also shown that enriched 15N could be detected in the shoot after a 1-h incubation of the root-system. It is concluded that the measurement of H2 evolution in combination with C2H2 reduction represents a nondestructive assay for nitrogen fixation in a Frankia symbiosis which shows no detectable hydrogenase activity.
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  • 18
    ISSN: 1432-2048
    Keywords: Glutamate synthase ; Glutamine synthetase ; Nitrogen fixation ; Phaseolus (glutamate synthase) ; Plastid (glutamate synthase) ; Root nodule
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The two isoenzymes of NADH-dependent glutamate synthase (NADH-GOGAT; EC 1.4.1.14), previously identified in root nodules of Phaseolus vulgaris L., have both been shown to be located in root-nodule plastids. The nodule specific NADH-GOGAT II accounts for the majority of the activity in root nodules, and is present almost exclusively in the central tissue of the nodule. However about 20% of NADH-GOGAT I activity is present in the nodule cortex, at about the same specific activity as this isoenzyme is found in the central tissue. Glutamine synthetase (GS; EC 6.3.1.2) occurs predominantly as the γ polypeptide in the central tissue, whereas in the cortex, the enzyme is represented mainly by the β polypeptide. Over 90% of both GS and NADH-GOGAT activities are located in the central tissue of the nodule and GS activity exceeds NADH-GOGAT activity by about twofold in this region. Using the above information, a model for the subcellular location and stoichiometry of nitrogen metabolism in the central tissue of P. vulgaris root nodules is presented.
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  • 19
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    Theoretical and applied genetics 71 (1986), S. 724-729 
    ISSN: 1432-2242
    Keywords: Nitrogen fixation ; Alfalfa cultivars ; Rhizobium strains ; Acetylene reduction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Two experiments were conducted in the greenhouse to study the interaction between alfalfa cultivars (Medicago sativa L. and M. falcata L.) and strains of Rhizobium meliloti Dang. for acetylene reduction rate, plant height and dry weights of shoot, root and whole plant. Fifteen alfalfa cultivars were inoculated with 10 strains of Rhizobium in Experiment I. Variance component analysis revealed that more than 30% of the total variance was due to alfalfa cultivars for acetylene reduction rate and 26% was accounted for by Rhizobium strains. More than 36% of the total variation was attributed to the interaction between alfalfa cultivars and Rhizobium strains for this character. Twenty-five host cultivars and 11 Rhizobium strains were included in Experiment II. The results also showed that the interaction of alfalfa cultivars and Rhizobium strains contributed the largest portion of the total variation for dry weights of shoot, root and whole plant and acetylene reduction rate. The results clearly demonstrated that the non-additive effects were the major component of variation for these characters associated with nitrogen fixation in alfalfa. Therefore, an effective way of improving nitrogen fixation in alfalfa is to select for a favourable combination of specific Rhizobium strains and alfalfa cultivars.
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  • 20
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    Theoretical and applied genetics 78 (1989), S. 433-435 
    ISSN: 1432-2242
    Keywords: Rhizobium ; Irradiation ; Nitrogen fixation ; Vicia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Sumary The objective of this work was to know the behaviour and variability of Rhizobium leguminosarum after irradiation. The induced variation was tested under greenhouse conditions on the variety JV 3 of broad beans (Vicia faba) in six replications. Induced genetic variabilty was observed for strain, parent and mutant versus parent. Out of 24 irradiated strains, strain 93-32 performed better with a greater number of nodules and higher dry weight of nodules per plant and biological yield. Environment played an important role in the expression of characters observed. High heritability and genetic advance of these traits indicated that the nitrogen fixation ability of Rhizobium can easily be improved by selection.
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  • 21
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    Molecular genetics and genomics 216 (1989), S. 484-491 
    ISSN: 1617-4623
    Keywords: Nitrogen fixation ; nifL ; Repression ; Metal ions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The ability of the Klebsiella pneumoniae nifL gene product to antagonise NIFA mediated transcriptional activation from the nifH promoter in vivo was inhibited either by metal deprivation, or by the presence of the iron chelators EDDA or Desferal in the growth medium. This inhibition of the repressive activity of NIFL was reversed by the addition of ferrous or manganous ions to the medium but was unaffected by other transition metals. The dependence on metal ions for NIFL activity was observed when NIFL was overexpressed and when cultures were exposed to oxygen or high levels of fixed nitrogen. Immunochemical evidence suggests that NIFL and NIFA associate to form a functional protein complex. Metal ions are apparently not required for the formation of this complex.
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  • 22
    ISSN: 1617-4623
    Keywords: glnB ; Klebsiella pneumoniae ; Nitrogen control ; Glutamine synthetase ; Nitrogen fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The role of theKlebsiella pneumoniae PII protein (encoded byglnB) in nitrogen regulation has been studied using two classes ofglnB mutants. In Class I mutants PII appears not to be uridylylated in nitrogen-limiting conditions and in Class II mutants PII is not synthesised. The effects of these mutations on expression from nitrogen-regulated promoters indicate that PII is not absolutely required for nitrogen control. Furthermore the uridylylated form of PII(PII-UMP) plays a significant role in the response to changes in nitrogen status by counteracting the effect of PII on NtrB-mediated dephosphorylation of NtrC. PII is not involved in thenif-specific response to changes in nitrogen status mediated by NifL.
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  • 23
    ISSN: 1617-4623
    Keywords: Archaebacteria ; Methanococcus voltae ; Nitrogen fixation ; Nitrogenase ; Fe protein gene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In Methanococcus voltae, a 3.0 kbp HindIII fragment carrying homology to nifH was recently cloned. In Escherichia coli maxicells, the fragment directed the synthesis of a 30 K polypeptide encoded by the region homologous to nifH. Plasmids carrying the fragment did not complement Klebsiella pneumoniae nifH mutants and did not inhibit the nitrogen fixation of a Nif+ strain. The complete nucleotide sequence of the nifH homologous region was determined. It contained an open reading frame (ORFnifH) of 834 bp encoding 278 amino acid residues (mol. wt. 30,362). The ORFnifH was surrounded by regions of very high A+T content as observed with other mc. voltae genes. The region upstream from ORFnifH contained potential prokaryotic-like promoters and a potential ribosome binding site located 5 bp preceding the translation initiation codon. Using a translational fusion to lacZ of a DNA fragment carrying the putative promoter region and the 5′ end of ORFnifH, it was shown in E. coli that (i) a promoter activity was effectively carried by the cloned fragment and (ii) this activity was not significantly modified by the presence of nifA or ntrC products provided by multicopy plasmids. Though the codon usage was characteristic of Mc. voltae, ORFnifH was very similar to eubacterial nifH genes, in particular the position of the cysteine residues was highly conserved. These data confirmed the high conservation of nifH sequences. SAB values (binary matching coefficients) of 0.5 were found with eubacterial nifH genes at the nucleotide or amino acid level suggesting that the mc. voltae ORFnifH sequence was distantly related to eubacterial nifH sequences.
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  • 24
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    Molecular genetics and genomics 205 (1986), S. 442-445 
    ISSN: 1617-4623
    Keywords: Rhodobacter capsulatus ; Nitrogen fixation ; Regulation ; nifA-like gene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A 15.2 kb DNA fragment was isolated from Rhodobacter capsulatus (ex. Rhodopseudomonas capsulata), which was able to complement mutations both in a nifA-like regulatory gene and in the nifH gene. Physical mapping of this fragment revealed that the nifA-like gene was adjacent to, and downstream from, the nifHDK operon. Hybridization experiments were carried out using a cloned Klebsiella pneumoniae DNA fragment containing nifA and the flanking portions of nifB and nifL. This fragment failed to hybridize with a 2.15 kb HindIII fragment of R. capsulatus DNA containing the nifA-like gene, but hybridized instead with a 2.6 kb EcoRI fragment adjacent to the nifA-like gene. The homologous region was found to be located within the K. pneumoniae nifB gene. The adjacent 2.6 kb and 2.15 kb fragments also hybridized with each other, indicating the presence of repeated sequences in this region.
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  • 25
    ISSN: 1617-4623
    Keywords: Nitrogen fixation ; nifL ; nifA ; Klebsiella oxytoca ; DNA sequence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The complete nucleotide sequence of the regulatory operon nifLA of a nitrogen fixer Klebsiella oxytoca NG13 was determined, and the transcriptional start point was assigned by S1 mapping. The nifL protein (a repressor) was coded by an open reading frame of 1,485 bases, corresponding to a protein of 495 amino acids with a calculated molecular weight of 55,242. The open reading frame (1,572 bases) of the nifA protein (an activator), corresponding to a molecular weight of 58,649, was confirmed by in vitro transcription-translation experiments, using the wild type and artificially deleted nifA genes. The initiation codon (ATG) of nifA overlapped the termination condon(TGA) of nifL, sharing the two bases T and G. A conserved DNA contact point [Gln-(X)3-Ala-(X)3-Gly-(X)5-Val] common in many DNA binding proteins was found in the C-terminal region of the nifA sequence. The promoter sequences of nifLA, nifB and nifF in K. oxytoca coincided exactly with those of K. pneumoniae in the consensus regions at-12 and-26, although the overall homology in the promoter regions was 96%. Changes of four amino acids were found between the nifA coding sequences of K. oxytoca and K. pneumoniae.
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  • 26
    ISSN: 1617-4623
    Keywords: Rhodobacter capsulatus ; Nitrogen fixation ; DNA sequence analysis ; nifE, nifN, nifX genes ; Protein comparisons
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Rhodobacter capsulatus genes homologous to Klebsiella pneumoniae nifE, nifN and nifX were identified by DNA sequence analysis of a 4282 bp fragment of nif region A. Four open reading frames coding for a 51188 (NifE), a 49459 (NifN), a 17459 (NifX) and a 17472 (ORF4) dalton protein were detected. A typical NifA activated consensus promoter and two imperfect putative NifA binding sites were located in the 377 bp sequence in front of the nifE coding region. Comparison of the deduced amino acid sequences of R. capsulatus NifE and NifN revealed homologies not only to analogous gene products of other organisms but also to the α and β subunits of the nitrogenase iron-molybdenum protein. In addition, the R. capsulatus nifE and nifN proteins shared considerable homology with each other. The map position of nifX downstream of nifEN corresponded in R. capsulatus and K. pneumoniae and the deduced molecular weights of both proteins were nearly identical. Nevertheless, R. capsulatus NifX was more related to the C-terminal end of NifY from K. pneumoniae than to NifX. A small domain of approximately 33 amino acid residues showing the highest degree of homology between NifY and NifX was also present in all nifB proteins analyzed so far. This homology indicated an evolutionary relationship of nifX, nifY and nifB and also suggested that NifX and NifY might play a role in maturation and/or stability of the iron-molybdenum cofactor. The open reading rame (ORF4) downstream of nifX in R. capsulatus is also present in Azotobacter vinelandii but not in K. pneumoniae. Interposon-induced insertion and deletion mutants proved that nifE and nifN were necessary for nitrogen fixation in R. capsulatus. In contrast, no essential role could be demonstrated for nifX and ORF4 whereas at least one gene downstream of ORF4 appeared to be important for nitrogen fixation.
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  • 27
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    Protoplasma 150 (1989), S. 19-26 
    ISSN: 1615-6102
    Keywords: Nitrogen fixation ; Peanut ; Root nodules ; Dense body ; Microbody ; Oleosome
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Nitrogen-fixing peanut root nodules are characterized by their unique structural organization, distinct from other legume nodules. The focus of this study has been in and around the hostsymbiont interface, where the bacterioid and the host cell surface (peribacteroid membrane envelope) interact during symbiosis. The infected nodule cells have revealed the presence of lipid bodies (oleosomes) in intimate association with the peribacteroid membrane, which encloses the large spherical bacteroids with a relatively narrow peribacteroid space. Electron dense structures, referred to as dense bodies have been found attached to the bacteroid outer membranes at the host-symbiont interface. The dense bodies are osmiophilic, amorphous and 3,3′-diaminobenzidine positive. The isolated intact bacteroids with dense bodies attached to their cell wall showed significant catalase activity. Many microbodies showing DAB-positive reaction have been found in the host cytoplasm, associated closely with the peribacteroid membrane. These ultrastructural and cytochemical characteristics of peanut root nodules suggest that lipids are utilized during symbiosis and the dense bodies and microbodies may be involved in the catabolic process.
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  • 28
    ISSN: 1615-6102
    Keywords: Plectonema boryanum ; Cyanobacteria ; Ultrastructure ; Nitrogen fixation ; Nitrogen starvation ; Immunogold localization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The ultrastructure of fructose-supplemented and unsupplemented nitrogen-fixing (fix +) and nonfixing (fix −)Plectonema boryanum UTEX 581 cells was examined by transmission electron microscopy. The most prominent structural differences included the arrangement and morphology of the thylakoids and alterations in the appearance of the interthylakoidal spaces. These ultrastructural differences, together with other observations such as glycogen content and presence of nitrogenase (using acetylene reduction assay and immunogold localization), readily distinguished nonfixingP. boryanum from nitrogen-fixing cells.
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  • 29
    ISSN: 1615-6102
    Keywords: Legumes ; Nitrogen fixation ; Nodulation ; Rhizobium ; Symbiosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Two methods have been developed in order to discriminate between lateral roots, nodules and root-derived structures which exhibit both root and nodule histological features and which can develop on legumes inoculated with certainRhizobium mutants. The first method, known as the “clearing method”, allows the observation by light microscopy of cleared undissected root-structures. The second, known as the “slicing method”, is a complementary technique which provides a greater degree of structural information concerning such structures. The two methods have proved invaluable in defining unequivocally the nature of the interaction between a rhizobial strain and a legume host.
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  • 30
    ISSN: 1617-4623
    Keywords: Rhizobium leguminosarum ; Nitrogen fixation ; nif/fix genes ; Escherichia coli minicells ; Transcription regulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary On the Rhizobium leguminosarum PRE sym plasmid, fixABC and a novel gene fixW were identified upstream of the regulatory gene nifA. The molecular masses of FixABC, 29, 44 and 50 kDa respectively, were estimated by polyacrylamide gel electrophoresis (PAGE) and of FixW, 25 kDa, by PAGE and nucleotide sequencing. Hybridization studies using bacteroid mRNA as a probe showed that fixABC is one operon which can be transcribed independently of fixW. Nucleotide sequencing revealed that both fixW and fixA are preceded by a nif consensus promoter. The fixA promoter partly overlaps the 3′-terminal coding region of fixW, indicating that readthrough from fixW into fixA is possible. Two open reading frames, ORF71 and ORF79, precede fixW and form one operon with fixW. ORF71 contains sequences homologous to the fixA promoter and 5′-terminal coding region. One more duplication of fixA sequences was detected, also located within the sym plasmid nif/fix clusters. One duplication of fixW sequences was found. No fixW homologue could be found in other nitrogen fixing organisms except in a number of R. leguminosarum strains.
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  • 31
    ISSN: 1617-4623
    Keywords: Nitrogen fixation ; draT ; draG ; TTG initiation codon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Nitrogen fixation activity in the photosynthetic bacterium Rhodospirillum rubrum is controlled by the reversible ADP-ribosylation of the dinitrogenase reductase component of the nitrogenase enzyme complex. This report describes the cloning and characterization of the genes encoding the ADP-ribosyltransferase (draT) and the ADP-ribosylglycohydrolase (draG) involved in this regulation. These genes are shown to be contiguous on the R. rubrum chromosome and highly linked to the nifHDK genes. Sequence analysis revealed the use of TTG as the initiation codon of the draT gene as well as a potential open reading frame immediately downstream of draG. The mono-ADP-ribosylation system in R. rubrum is the first in which both the target protein and modifying enzymes as well as their structural genes have been isolated, making it the model system of choice for analysis of this post-translational regulatory mechanism.
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  • 32
    ISSN: 1617-4623
    Keywords: Frankia ; Nif genes ; Nitrogen fixation ; Plasmid ; Actinorhizal symbiosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We report that in DNA from one Frankia sp. strain at least some of the nif genes are located on a large indigenous plasmid of 190 kb. Using the cloned nitrogenase structural genes from Klebsiella pneumoniae as hybridization probes, homology was detected with a 5.6 kb EcoRI fragment from the Frankia sp. plasmid. This 5.6 kb fragment was cloned; used as a probe it hybridized to the nif K, D and H genes from Rhizobium meliloti and Klebsiella pneumoniae. The nif probes also hybridized on total DNA blots to a 10 kb EcoRI fragment that is not present on plasmid DNA, suggesting that the nif genes could be located on more than one replicon.
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  • 33
    ISSN: 1617-4623
    Keywords: Nitrogen fixation ; nif genes ; Azotobacter vinelandii ; Tn5 mutants ; Gene banks
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Tn5 was introduced into Azotobacter vinelandii on a suicide vector, pGS9. Three Nif- mutants were found to carry Tn5 in nifH (MV6), in nifN (MV22), and in or near nifM (MV21), from the results of hybridisation experiments. For MV21 and MV22 this was also shown by complementation with the nif genes of Klebsiella pneumoniae on pRD1. MV6 failed to synthesis the nifH, D and K gene products. MV6 and MV22 fixed nitrogen in the absence of supplied molybdenum while mutant MV21 did not, suggesting that the nifM gene product may be required for the alternative nitrogenase system synthesised in azotobacteria under conditions of molybdenum deprivation. Reconstitution experiments with mutant extracts showed that MV22 (nifN -) lacked the FeMo cofactor and that MV21 (NifM-) synthesised inactive Fe protein. These biochemical phenotypes are identical to those of the K. pneumoniae nifN and nifM mutants, respectively, demonstrating that these genes have the same function in both K. pneumoniae and A. vinelandii. Complementation of the A. vinelandii mutants with pLAFR1 gene banks of A. vinelandii or a. chroococcum yielded three cosmids of interest. pLV10 complemented UW91, a nifH mutant, and corrected the defect in MV6 after recombination with the mutant genome. It also carried nifD (but not nifK) and about 18 kb of DNA upstream from nifH. pLV1 from the A. vinelandii gene bank complemented both MV21 and MV22 as did pLC11, isolated from the A. chroococcum gene bank. Both pLV1 and pLC11 carried part of the nif cluster downstream of nifHDK which also includes nifEN and nifMVS on about 22 kb of DNA.
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  • 34
    ISSN: 1617-4623
    Keywords: Anabaena doliolum ; Sporulation ; Mutants ; Nitrogen fixation ; Cell constituents
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Mutants of Anabaena doliolum (AdS strain) altered with respect to the time of initiation and degree of sporulation were isolated following mutagenesis with N-methyl-N′-nitro-N-nitrosoguanidine and hydroxylamine. The non-sporulating mutant showed a high phycocyanin (Pc): chlorophyll a (chl a) ratio (ca. 7.2) as compared to sporulating strains (Pc:chl a, 4.7–5.3). Also this strain seemed to have higher RNA pools per unit of genomic material as reflected in a higher RNA:DNA ratio. The data suggest that degradaton of phycocyanin and controlled RNA synthesis are prerequisites for sporulation. Mutants exhibiting non-sporulation and delayed initiation of sporulation accumulated more nitrogen through nitrogen fixation, probably indicating nitrogenase function over an extended vegetative phase.
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  • 35
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    Molecular genetics and genomics 215 (1989), S. 507-516 
    ISSN: 1617-4623
    Keywords: Nitrogen fixation ; Regulation ; Rhodobacter capsulatus ; Gene sequences ; Transcription factors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We have determined the DNA sequence for the genes nifR1, nifR2 and nifR4 in the photosynthetic bacterium Rhodobacter capsulatus. These genes regulate transcription of the nifHDK operon and so limit the expression of nitrogen fixation activity to periods of low environmental concentrations of both oxygen and fixed nitrogen. The sequences of these three genes are similar to components of the ntr regulation system in Escherichia coli and Klebsiella pneumoniae. The two-component regulatory system of ntrB and ntrC in E. coli is represented by nifR2 and nifR1 in R. capsulatus and nifR4 in R. capsulatus is the equivalent of the E. coli ntr-related sigma factor ntrA.
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  • 36
    ISSN: 1573-5036
    Keywords: Cowpea ; Nitrogen fixation ; Nodulation ; Pea ; Pesticide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Six carbamate pesticides namely 1-naphthol, sevin, dimetilan, trematan, NaDDC and dymid were studied to see their effect on nodulation and nitrogen fixation inPisum sativum andVigna sinensis. Low concentrations of the pesticides have little effect on nodulation and nitrogen fixation, whereas higher concentrations adversely effect these processes. The results also indicate that then sensitivity depends upon the species of the Rhizobium and also the type of the pesticide. Pesticides belonging to the carbamate group differ in their capacity to affect nodulation and nitroge fixation.
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  • 37
    ISSN: 1573-5036
    Keywords: Mycorrhiza ; Nitrogen fixation ; Nodulation ; Soybean ; Symbioses
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Glycine max (L. Merr. cv. Amsoy 71) plants were grown in a greenhouse in a sand/perlite medium low in plant-available N and P. Plants were either inoculated with a vesicular-arbuscular mycorrhizal (VAM) fungus alone, a strain ofRhizobium japonicum alone, both endophytes together or were left non-inoculated to serve as a control. All combinations received a N-and P-free nutrient solution. Nodulated plants contained 4 to 5 times the phytomass of non-inoculated controls, and plants colonized with both the VAM fungus and Rhizobium were 18% greater in dry weight than nodulated, non-VAM plants due to a positive VAM times Rhizobium interaction. Nitrogen fixation, calculated from C2H4 and H2 data, was significantly higher in the tripartite symbiosis, with 80% of the increase attributable to increased nodule mass and 20% due to increases in specific nodule activity. Colonization by the VAM fungus and the development of vesicles increased significantly following nodulation. The synergistic interactions between the microsymbionts suggests that the response of the host to dual colonization is complex and depends on a balance between the three members of the symbiosis.
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  • 38
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    Plant and soil 92 (1986), S. 55-62 
    ISSN: 1573-5036
    Keywords: Acetylene reduction ; Environmental factors ; Low temperature ; Nitrogen fixation ; Rhizobium ; Trifolium pratense
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Red clover Rhizobium strains, isolated from different locations between latitudes 60° and 63°30′ N in Finland, were tested for their adaptation to low temperatures. 31 strains were tested for growth at 5°C, 10°C, 15°C and 18°C in pure culture. No strain grew at 5°C. At the other temperatures there were differences between the strains, but the same strains grew fast at all temperatures. Ten strains were investigated for nodulation and acetylene reduction in phytotrons in two different climates, one simulating the growing season in southern and the other in northern Finland. There were differences between the strains in their ability to nodulate their host plant, and northern strains showed higher nitrogenase activity than southern strains in the cold climate.
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  • 39
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    Plant and soil 92 (1986), S. 171-180 
    ISSN: 1573-5036
    Keywords: Acetylene reduction ; Associative nitrogen fixation ; Azospirillum ; Nitrogen fixation ; Wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Spring-wheat plant seedlings were inoculated with various isolates of nitrogen-fixing rhizosphere bacteria, includingAzospirillum brasilense, in gnotobiotic sand cultures. Bacteria which had lost their acetylene reduction activity (ARA) during purification did not regain it in the presence of the plant. Bacteria with stable ARA were stimulated to low ARA (maximum 5.6 nmol C2H4 plant−1 h−1) by young (22–32-day) wheat seedlings.
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  • 40
    ISSN: 1573-5036
    Keywords: Combined nitrogen ; Grain yield ; Inoculation ; Nitrogen fixation ; Rhizobium leguminosarum ; Vicia faba
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Nitrogen limitations to the yield of a field crop ofVicia faba have been examined. Application of nitrogen totalling 560 kg/ha increased dry matter yield at flowering by 674 kg/ha (32%) and grain yield at final harvest by 1.6 tonnes/ha (24%). Attempts to reduce nitrogen limitations by replacing the native rhizobia with strains ofRhizobium leguminosarum selected for high rates of nitrogen fixation were unsuccessful but the introduction of poor rhizobia reduced grain yield. The reasons for this and the implications of the results for crop improvement are discussed.
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  • 41
    ISSN: 1573-5036
    Keywords: Alfalfa ; Barley ; Corn ; Management ; Nitrogen ; Nitrogen fixation ; Plow down ; Red clover ; Sweetclover ; Temperate climate ; Trefoil
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Under some conditions the plow down of forage legumes increases the yield of subsequent crops, which is usually caused by improved soil N. However, better soil structure is also a contributing factor. Three experiments were conducted to measure the effect of legume plow down on the yield of subsequent corn crops grown at the Ottawa Research Station (ORS), Ottawa, Canada. In all experiments, corn yields were not affected by legume species, legume cultivars, and/or planting methods. Corn yields from barley plots receiving 0, 60, or 120 kg N ha−1 did not differ until two years after establishment in one experiment and three years in another. The data from these experiments indicated that soil N was high at the ORS, which may inhibit N2-fixation by forage legumès in the establishment year. Therefore, legume plow down was not beneficial to subsequent crops under these conditions. Two other experiments were conducted to measure the effect of legume plow down on the yield of subsequent barley crops. In both experiments, barley yields in the field were not affected by legume type or legume seeding density. Greenhouse and field data indicated that the two cuts with removal strategy benefitted the most to succeeding crops. Data from the greenhouse test indicated that soil N levels were not low in the establishment year, and that some cultivars improved soil fertility more than others.
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  • 42
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    Plant and soil 114 (1989), S. 63-68 
    ISSN: 1573-5036
    Keywords: Azolla pinnata ; Nitrogen fixation ; N yield ; Oryza sativa ; Urea-N
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Application of 0, 30, 60, 90 and 120 kg N ha−1 of urea (U) in split doses with (and without)Azolla pinnata, R. Brown was studied for three consecutive seasons under planted field condition. Fresh weight (FW), acetylene reduction activity (ARA) and N yield of Azolla were found to be maximum 14 days after inoculation (DAI). Among the different treatments, maximum Azolla growth was recorded in no N control. The FW, ARA and N yield of Azolla were inhibited increasingly with the increase in N levels. Irrespective of season, FW and N yield of Azolla were inhibited only a small extent with 90 kg N ha−1 U, beyond which the inhibition was pronounced. ARA was inhibited only slightly up to 60 kg N ha−1 of U. Grain yield and crop N uptake of rice increased significantly up to 90 kg N ha−1 of U (alone or in combination with Azolla) in the dry seasons (variety IR 36) and up to 60 kg N ha−1 U in the wet season (variety CR 1018).
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  • 43
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    Plant and soil 90 (1986), S. 141-150 
    ISSN: 1573-5036
    Keywords: Aromatic degradation ; Bacteria ; Nitrogen fixation ; Phenolics ; Physiology ; Soil
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary A microaerobic diazotrophic bacterium tentatively identified as aPseudomonas species was isolated from a forest soil. Its nitrogenase (C2H2 reduction) activity in liquid medium was significantly supported by phenolic compounds when compared with glucose-, mannitol- or malate-supported activity. The utilization of phenolics was dependent on substrate induction and the appropriate oxygen concentration. At a pO2 of 0.05 protocatechuate was a better carbon source for N2 fixation than glucose. In the case ofLignobacter protocatechuate was a better carbon source for N2 fixation than glucose at pO2 0.2 but not at pO2 0.05. It is suggested that certain monomeric phenols can support nitrogenase activities in many carbon-limited soil environments.
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  • 44
    ISSN: 1573-5036
    Keywords: Blue grass ; Klebsiella pneumoniae ; Poa pratensis ; Triticum aestivum ; Nitrogen fixation ; Nitrogen nutrition ; 15N isotope dilution ; Spring wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The technique of15N isotope dilution was used to verify that nitrogen was fixed and transferred to the plant byKlebsiella pneumoniae strain Pp in association withPoa pratensis orTriticum aestivum. Surface sterilized, sprouting seeds were inoculated withK. pneumoniae and grown in sand in modified Leonard jars. Potassium nitrate enriched with15N was used to provide N concentrations ranging from 10–40 mg Nl−1 nutrient solution. After 10–18 weeks the shoots and roots were analyzed separately for dry matter, N content, total N, and atom %15N excess. The acetylene reduction technique was used to test for the presence of N2-fixing organisms on the roots. The data from15N isotope dilution demonstrated that up to 33.8% of N in the shoots ofP. pratensis and 15.9% in those ofT. aestivum were derived from associative N2 fixation byK. pneumoniae. In most experiments the dry matter yield, N content, and total N yield of the shoots ofP. pratensis were increased byK. pneumoniae inoculation, whereas inoculation had no significant effect on the dry matter yield, N content or total N of the shoots ofT. aestivum.
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  • 45
    ISSN: 1573-5036
    Keywords: Brachiaria spp ; Nitrogen fixation ; 15N techniques ; Paspalum notatum ; Pasture grasses
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Six pasture grasses,Paspalum notatum cv batatais,P. notatum cv pensacola,Brachiaria radicans, B. ruziziensis, B. decumbens andB. humidicola, were grown in concrete cylinders (60 cm diameter) in the field for 31 months. The soil was amended with either a single addition of15N labelled organic matter or frequent small (2 kg N. ha−1) additions of15N enriched (NH4)2SO4. In the labelled fertilizer treatment soil analysis revealed that there was a very drastic change in15N enrichment in plant-available nitrogen (NO 3 − +NH 4 + ) with depth. The different grass cultivars recovered different quantities of applied labelled N, and evidence was obtained to suggest that the roots exploited the soil to different depths thus obtaining different15N enrichments in soil derived N. This invalidated the application of the isotope dilution technique to estimate the contribution of nitrogen fixation to the grass cultivars in this treatment. In the labelled organic matter treatment the15N label in the plant-available N declined at a decreasing rate during the experiment until in the last 12 months the decrease was only from 0.274 to 0.222 atom % excess. There was little change in15N enrichment of available N with depth, hence it was concluded that although the grasses recovered different quantities of labelled N, they all obtained virtually the same15N enrichment in soil derived N. Data from the final harvests of this treatment indicated thatB. humidicola andB. decumbens obtained 30 and 40% respectively of their nitrogen from N2 fixation amounting to an input of 30 and 45 kg N.ha−1 year−1 respectively.
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  • 46
    ISSN: 1573-5036
    Keywords: Azolla caroliniana (Willd.) ; Isotope dilution ; Nitrogen fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The symbiotic association of the water fernAzolla with the blue-green algaAnabaena azollae can fix 30–60 kg N ha−1 per rice cropping season. The value of this fixed N for rice production, however, is only realized once the N is released from theAzolla biomass and taken up by the rice plants. The availability of N applied asAzolla or as urea was measured in field experiments by two15N methods. In the first,Azolla caroliniana (Willd.) was labelled with15N in nutrient solution and incorporated into the soil at a rate of 144 kg N ha−1. The recovery ofAzolla-N in the above ground parts of rice [Oryza sativa (L) cv. Nucleoryza] was found to be 32% vs. 26% for urea applied at a rate of 100 kg N/ha; there was no significant difference in recovery. In the second, 100 kg N/ha of15N-urea was applied separately or in combination with either 250 or 330 kg N ha−1 of unlabelledAzolla. At the higher rate, the recovery ofAzolla-N was significantly greater than that of urea. There was a significant interaction when both N sources were applied together, which resulted in a greater recovery of N from each source in comparison to that source applied separately. Increasing the combined urea andAzolla application rate from 350 kg N ha−1 to 430 kg N ha−1 increased the N yield but had no effect on the dry matter yield of rice plants. The additional N taken up at the higher level of N application accumulated to a greater extent in the straw compared to the panicles. Since no assumptions need to be made about the contribution of soil N in the method using15N-labelledAzolla, this method is preferable to the15N dilution technique for assessing the availability ofAzolla-N to rice. Pot trials usingAzolla stored at −20°C or following oven-drying showed that both treatments decreased the recovery of N by one third in comparison to freshAzolla.
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  • 47
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    Plant and soil 90 (1986), S. 335-342 
    ISSN: 1573-5036
    Keywords: Azospirillum brasilense ; Effect on yield ; Inoculation ; Legumes ; Nitrogen fixation ; Rhizobium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Inoculation of naturally nodulatedPisum sativum L. (garden pea) withAzospirillum in the greenhouse caused a significant increase in nodule numbers above controls. Field inoculation of garden peas in the winter 1981–1982 andCicer arietinum L. (chick pea), in winter 1982–1983, withAzospirillum one week after plant emergence, produced a significant increase in seed yield, but did not affect plant dry matter yield. ForVicia sativa L. (vetch) grown in soil in the greenhouse and in the field for forage, winter 1980–1981, inoculation significantly increased dry matter yield, %N, N-content, and acetylene reduction (nitrogen fixation) activity. InHedysarum coronarium L. (sulla clover), winter 1981–1982, inoculated with both its specificRhizobium (by the slurry method) andAzospirillum, 7 days after emergence, there was an increase in acetylene reduction above controls inoculated withRhizobium alone. These results suggest that it is possible, under conditions tested in this work, to increase nodulation, nitrogen fixation, and crop yields of winter legumes by inoculation withAzospirillum.
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  • 48
    ISSN: 1573-5036
    Keywords: A-value ; Barley ; Field bean ; Isotope dilution ; Nitrogen fixation ; 15N ; Non-fixing reference crop ; Pea ; Pisum sativum ; Vicia faba
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The total amount of nitrogen derived from symbiotic nitrogen fixation in two pea and one field bean cultivar, supplied with 50 kg N ha−1 at sowing (‘starter’-N), was estimated to 165, 136, and 186 kg N ha−1, respectively (three-year means). However, estimates varied considerably between the three years. At the full bloom/flat pod growth stage from 30 to 59 per cent of total N2 fixation had taken place. The proportion of total N derived from N2 fixation at maturity was higher in seeds than in vegetative plant parts and amounted to 59.5, 51.3 and 66.3 per cent of total above-ground plant N in the two pea cultivars and field bean, respectively (three-year means). The recovery of fertilizer N was 62.2, 70.2, 52.1, and 69.5 per cent in the two pea cultivars, field bean and barley, respectively. Growth analysis indicated that barley did not meet the claims for an ideal reference crop in the15N fertilizer dilution technique for estimating N2 fixation in pea and field bean. ‘Starter’-N neither increased the seed yield nor the N content of the grain legumes.
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  • 49
    ISSN: 1573-5036
    Keywords: Nitrogen fixation ; Nucleotide pools ; Rhodospirillum rubrum ; Switch off
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary When ammonium ions are added to a nitrogen fixing culture ofRhodospirillum rubrum, nitrogenase activity decreases due to inactivation of the Fe-protein. We have studied the adenylate and pyridine nucleotide pools during switch-off using the sensitive bioluminescence method. Immediately after the addition of ammonium ions there is a decrease in the ATP pool which is quickly reversed and no change is seen during the switch-off period. The pyridine nucleotide pools also do not change significantly during the switch-off. Consequently we conclude that changes in the pools studied were not the signal promoting inactivation of the Fe-protein.
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  • 50
    ISSN: 1573-5036
    Keywords: Alnus rubra ; Alnus glutinosa ; Fatty acids ; Frankia ; Nitrogen fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Alnus species are used widely in Britain for land reclamation, forestry and other purposes. Rapid juvenile growth of the AmericanAlnus rubra makes it an attractive species for planting on N-deficient soils, particularly those of low organic content. In small plot trials, this species is nodulated by indigenous soil frankiae as effectively asAlnus glutinosa. Over a three year period both species return similar amounts of N to the ecosystem, estimated at up to 10–12 kg N ha−1. Several strains ofFrankia have been isolated from local (Lennox Forest)A. rubra nodules. These differ morphologically and in their growth on different culture media, both from each other and fromA. glutinosa nodule isolates. AllAlnus isolates, however, have a total cellular fatty acid composition qualitatively similar to some other Group B frankiae. Glasshouse tests in N free culture suggest thatA. rubra nodules formed after inoculation of seedlings with American spore (−) isolates are three times more effective in N fixation than those inoculated with LennoxA. rubra spore (+) nodule homogenates. By contrast, the early growth of seedlings inoculated with spore (−)Frankia strains suggests at best a 35% improvement in N fixing activity over seedlings inoculated with LennoxA. rubra nodule isolates. Nevertheless, this improvement in activity, together with the better performance of seedlings inoculated with isolates compared with those treated with crushed nodule preparations, suggest that it would be worthwhile commercially to inoculate nursery stock with a spore (−)Frankia strain.
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  • 51
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    Plant and soil 90 (1986), S. 429-453 
    ISSN: 1573-5036
    Keywords: Actinorhizae ; Frankia ; Genetics ; Nitrogen fixation ; Nodulation ; Symbiosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 52
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    Plant and soil 91 (1986), S. 43-49 
    ISSN: 1573-5036
    Keywords: Alnus incana ; Frankia ; Leaf litter ; Nitrogen fertilization ; Nitrogen fixation ; Root exudation ; Root litter ; Shoot litter
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary A pot experiment withAlnus incana (L.) Moench growing in sand was set up to compare the amounts of nitrogen released from plants shoot litter with that released below ground as root litter and/or root exudation. No nitrogen fixation by free-living microorganisms was found in the sand and the increased nitrogen content of the plant + soil system was therefore due to nitrogen fixation byFrankia in the alder root-nodules. Most of the nitrogen released from the plants was in the nitrogen-rich leaf and other shoot litter. Only small amounts of nitrogen were found in the drainage water from the pots and were recorded as increased nitrogen content of the sand.
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  • 53
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    Plant and soil 91 (1986), S. 147-160 
    ISSN: 1573-5036
    Keywords: Cowania ; Frankia ; Microbial ecology ; Nitrogen fixation ; Purshia ; Revegetation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Nitrogen fixing trees and shrubs may be useful in revegetation efforts. The possibility that soil and environmental factors may influence a soil's capability to produce nodulated seedlings was explored.Purshia tridentata andCowania mexicana var. Stansburiana seedlings were grown in greenhouse trials using ten soils from native sites for each of the two genera. Treatments included a control and a six mmole nitrogen amendment as NH4NO3 for both surface and subsurface samples. Nodulation was often sparse for seedlings grown in surface collected samples. Although nodulation was usually better in subsoil samples, even some subsoils produced few or no nodules. Nitrogen additions inhibit nodulation and although soil nitrogen may be inhibitory in some unamended surface soils it is probably not a general cause of sparse nodulation. Nodule masses showed the same trends as nodule number but varied less with treatment and depth of soil source. Seedlings compensated for sparse nodulation with an increase in mass per nodule. Incidence of nodulation was related to some soil and environmental factors. Multiple regression analysis explained a substantial portion of nodulation variability. Soils from lower elevations with less precipitation did not produce well nodulated seedlings even in well watered greenhouse trials. Micronutrient cations, potassium, and phosphorus are positively correlated with nodulation incidence. The two genera were generally similar in nodulation responses to soil and environmental factors.
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  • 54
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    Plant and soil 92 (1986), S. 249-254 
    ISSN: 1573-5036
    Keywords: Ecology ; Nitrogen fixation ; Rhizobium leguminosarum populations ; Vicia faba
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The size and symbiotic effectiveness, withVicia faba, ofRhizobium leguminosarum populations from five locations in southern Britain has been estimated. Population numbers varied from 4.54×103 to 1.69×105. Nitrogen fixing potential differed by up to 30%. The implications of the results for improving the productivity of field beans are discussed.
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  • 55
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    Plant and soil 94 (1986), S. 147-151 
    ISSN: 1573-5036
    Keywords: Nitrogen fixation ; 15N Rhizobia ; Vigna radiata ; Nitrogen
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Remobilization of15N from vegetative tissue of mungbean (Vigna radiata (L.) Wilczek) into pods was measured during the reproductive phase of growth. Plant tissue was labelled with15N during vegetative development. Experiments were conducted in the field at two sites. At one site the soil provided cowpeas with most of their N but at the other site N fixation provided most of the N. Remobilized N from vegetative tissue to pods occurred soon after they began to develop. The quantity of the labelled N ultimately remobilized to the pods amounted to 50% for one cultivar (Tx33) at the high soil N site and 70% at the low N site. For the other cultivar (Tx13) the values were 25% and 30%, respectively. The two cultivars performed very differently with respect to partitioning of N into pods and the rate of N fixation. Even though more N was accumulated in the shoots of the high N fixing cultivar (Tx13) less total N was contained in the pods.
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  • 56
    ISSN: 1573-5036
    Keywords: Fertilizer ; Lupinus ; Nitrogen ; Nitrogen fixation ; Nutrient availability ; Pinus ; Water potential
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The effects ofLupinus angustifolius, L. arboreus. and nitrogen fertilizer plus weedicide on soil inorganic nitrogen, and the growth, nutrition and water status ofPinus radiata seedlings were compared on a sandy podzol in Victoria Australia. Both lupins increased the concentration of soil inorganic nitrogen from 6 μg g−1 to at least 11 μg g−1 one year after treatment.Lupinus arboreus (a perennial) led to high mortality ofP. radiata seedlings and no growth response in survivors because it competed for water during summer. In contrast,L. angustifolius (an annual) senesced prior to summer and resulted in increased fascicle size and stem growth rates ofP. radiata. Growth ofP. radiata withL. angustifolius was similar to that with weedicide only. The concentration. of phosphorus in foliage ofP. radiata seedlings was highest when growth withL. angustifolius. However, the highest growth rate ofP. radiata occurred in the nitrogen fertilizer plus weedicide treatment.
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  • 57
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    Plant and soil 95 (1986), S. 301-313 
    ISSN: 1573-5036
    Keywords: Alnus glutinosa ; Ammonium ; Nitrate ; Nitrate reductase activity ; Nitrogen fixation ; Phyllosphere
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Thein vivo nitrate reductase activity (NRA) was determined inAlnus glutinosa plants grown nonsymbiotically on ammonium, nitrate, a combination of both, or symbiotically with atmospheric nitrogen as the only nitrogen source. Root NRA was absent when ammonium or atmospheric nitrogen was the nitrogen source. With nitrate in the culture solution the roots showed a high NRA. However, the leaf NRA behaved quite differently: with negligible activities on all nitrogen sources except atmospheric nitrogen. The foliar NRA measured, however, is likely not due to the activity of the plant but of microbial origin. Methods commonly used to facilitate produced nitrite to leak out of the tissue, such as addition of propanol and cutting the plant material, did not increase the nitrite release from the leaves. A turbidity developed when testing the samples for nitrite which was positively correlated with the NRA. Populations of microorganisms in the phyllosphere did not differ between the nutritional treatments. Bacteria, able to grow on a low-nitrogen medium, were present on the leaves. Nitrifiers could not be detected. The bacteria on the leaves appear to produce nitrite when incubated with leaf material.
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  • 58
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    Plant and soil 96 (1986), S. 17-29 
    ISSN: 1573-5036
    Keywords: Drought stress ; Growth ; Harvest ; Legume ; Medicago sativa L. ; Nitrogen fixation ; Nitrogen assimilation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Symbiotic N2 fixation, NO 3 − assimilation and protein accumulation in the shoots were measured simultaneously in alfalfa (Medicago sativa L.) grown in the field or in pots, in order to study how the balance between the two modes of nitrogen nutrition could be influenced by agronomic factors, such as harvest, mineral nitrogen supply and drought stress. During periods of rapid growth, fixation and assimilation may function simultaneously; they are antagonistic at the beginning and at the end of the growth cycle, when the nitrogen requirement of the plant is lower. When nitrogen nutrition does not limit growth, mineral nitrogen supply favours assimilation at the expense of fixation, but does not modify the amount of nitrogen accumulated, which is adjusted to the growth capacity of the plant. After cutting, nitrate assimilation compensated for the decrease in fixation and supplied the plant with the nitrogen required by the regrowth, the proliferation of which determined the fixation recovery. Drought stress decreased N2 fixation much more than NO 3 − assimilation. The latter made growth recovery possible when water supply conditions became normal again. These results suggested the existence of an optimum level of nitrate assimilation, which differed depending on the age of the plants and allowed both maximum growth and fixing activity.
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  • 59
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    Plant and soil 96 (1986), S. 205-213 
    ISSN: 1573-5036
    Keywords: Actinorhizal plants ; Alnus glutinosa ; Alnus incana ; Frankia ; Nitrogen fixation ; Nodules
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The distribution of spore positive (Sp+) and spore negative (Sp−) nodules on the two native alder species (A. incana andA. glutinosa) in Finland was investigated. Nodules were collected throughout the country from different ecosystems (forests, swamps, lake- sea- and riversides, old pastures and fields as well as from alder plantations). OnA. incana Sp+ nodules predominated, whereas onA. glutinosa the vast majority of the nodules were of the Sp− type. Sp+ nodules onA. glutinosa were found only at sites where the two alder species grew close together. This distribution pattern indicates an association of nodule type with alder species, the reasons for which are discussed. Indications of saprophytic growth in the Sp− strain were also found.
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  • 60
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    Plant and soil 96 (1986), S. 215-224 
    ISSN: 1573-5036
    Keywords: Acetylene reduction ; Daviesia mimosoides ; Eucalypt forest ; Nitrogen fixation ; Nodulation ; Understorey
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Daviesia mimosoides is a common understorey legume in Eucalyptus forests of the Brindabella Range in southeastern Australia, capable of fixing atmospheric nitrogen. Rates of N fixation were measured by the acetylene-reduction technique over a growing season in the field. Pot trials under controlled conditions were also carried out to elucidate effects of soil moisture, temperature, and light. Average rates in the field varied from about 1–5 μ mol C2H4/g/h (wet weight of nodule), but rates up to 14 μ mol C2H4/g/h were measured in optimum controlled conditions. Annual N-fixation rates approximate 4.5–7.0 kg/ha. In pot trials, rate of acetylene reduction decreased with soil moisture to about−10 MPa tension, with a marked depression at about−6 MPa, but within the normal field range of soil moisture there was little correlation of moisture with average acetylene reduction rate. Rates were similar in the temperature range of 20–30°C, but were depressed by either low or high temperature (〈10 or 〉30°C). Diurnal fluctuations in acetylene reduction rates were not correlated with solar radiation, but rates were limited by high mid-day temperatures.
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  • 61
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    Plant and soil 96 (1986), S. 327-335 
    ISSN: 1573-5036
    Keywords: Isotope discrimination ; Macropitilium atropurpureum ; Nitrogen fixation ; Nitrogen transfer ; Panicum coloratum ; Rhizobia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Isotope dilution provides a method for measuring plant competition for mineral N and transfer of biologically fixed N from a legume to a grass. A plant growth medium was enriched with15N, and used to grow Siratro (Macropitilium atropurpureum D.C. Urb.) and Kleingrass 75 (Panicum coloratum L.) in 20 liter pots for 98 days in a glasshouse. The plants were grown in pure stand and in mixtures. When grown in 50∶50 mixture the grass obtained 59% of the labelled N and the legume obtained 41%. The grass produced nearly as much root mass as the legume even though biomass of the shoots were less than half that of the legume. Reducing the proportion of either plant species in the mixture reduced the proportion of the mineralized N absorbed by that species. The shoots of the grass were significantly more enriched (1.166 atom%15N excess) than the roots (1.036). The grass received 12% of its N as biologically fixed N from the legume.
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  • 62
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    Plant and soil 90 (1986), S. 193-202 
    ISSN: 1573-5036
    Keywords: azospirillum ; Denitrification ; Nitrate respiration ; Nitrite reductase ; Nitrogen fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Model experiments were performed to investigate the nitrogen fixation (C2H2 reduction) and denitrification (N2O formation) capabilities ofAzospirillum spp. in association with wheat. Plants and bacteria were grown together for a week and then assayed for activities. This association performed C2H2 reduction or N2O formation, depending on the concentrations of nitrate and oxygen in the vessels. Both activities depended on theAzospirillum strains used. The newly isolatedAzospirillum amazonense strains Y1 and Y6 showed significant C2H2 reduction and low N2O formation in association with wheat under the conditions employed and are possibly useful in practice. A cell-free preparation fromAzospirillum brasilense Sp 7 possessed a cytochrome cd type dissimilatory nitrite reductase.
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